Extruder stutters

Hi,

I've got a problem with my extruder, it stutters.
Yesterday I noticed some serious underextrusion and wanted to check the the e-steps, so I tried to extrude 100mm of filament (3mm PLA from print2beta at 200°C). Shortly after the extrusion started I noticed some stuttering noises. It extruded roughly 35mm of filament before the stuttering. While stuttering no filament is forced in the extruder. But when I start another extrusion process it starts extruding absolutely fine but does the same stuttering in the middle of the process. I cleaned the hobbed bolt and readjusted the gears and the pressure on the idler wheel. More pressure makes the stuttering even worse.
What could be the reason for this? I googled and found articles that blame the stepper drivers or the voltages for this, but since I use the latest nophead kit with the melzi and didn't make any fireware changes besides the z height I kind of doubt that this will be the point of failure. Are there other things I could test?

Thanks in advance!
Mathias

P.S.: The sound is similar to this (this is not my video and not my printer, just the same problem I guess) [www.youtube.com]

If the motor jumps backwards like the video it hasn't enough torque to push the filament. However it should have plenty, so perhaps the hot end is blocked or not hot enough. Or if the spring tension is too high the filament might be squashed flat and then be too wide for the hot end.

Turn the motors off and try extruding by hand. If it takes a lot of force try raising the temperature 20C.

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[www.hydraraptor.blogspot.com]

Might be worth removing the large gear to get at the hobbed bolt to see if it is 'bunged up' with filament debris between its teeth at some point as if the motor is turning with nothing coming out the other end, you are likely to be grinding away at the filament as the hobbled bolt tries to push it forwards.

Alan

Ok, I disassembled everything, cleaned the bolt and readjusted the extruder idler wheel. I tried to clean the hotend with a "cold pull" at 80°C as well, but couldn't no The stuttering is now gone but it still makes cracking noises after the same amount of filament (35mm) extruding. I tried a new spool of PLA and it is the same. Even higher temperatures like 220°C didn't change that. I must come from the hobbed bolt, but it only occurs after nearly 2 full rotations of the bolt. And it is gone after another 2 full rotations. It is also the same if I extrude the 100mm all at once or in steps of 10mm.

What speed are you extruding at? Perhaps it is simply too fast. 60mm/m is about the flow rate for building at 50mm/s. I think pronterface defaults to 300mm/m, which is crazy fast for 3mm filament.

I can't imaging what would prevent you doing a cold pull with PLA.

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[www.hydraraptor.blogspot.com]

I had a look at the speed and you were right, at 60mm/s it was not an issue at all. Right now it's printing again. Thank you very much!

After a month of successful printing, the stuttering is back. And now It seems to come from the gears. After I checked the gears and repositioned the small one, it extruded again. But after homing all axis the stuttering was back. When I changed the position of the small gear again, it extruded fine but never managed got get beyond the homing. It seems that a "motors of" command or something like that makes the extruder loose it's grip/strength. Could the fact that repositioning the small gear made a differences be an indicator for a worn out gear? How does a worn out gear look like? I can't really see any abrasion on the gears itself. Since I never managed to try ABS, I haven't printed any spare parts or anything, so I'm thinking about getting a new extruder unit (everything except the x carriage) to be able to print again and later on to have a separate one for each abs and pla.

When the gears wear out the teeth fall off!

Does the gear move forwards and then slip back a bit or does it vibrate on the spot?

If you disable the motor can you turn the gear by hand and extrude easily?

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[www.hydraraptor.blogspot.com]

Ok, so my gears are not worn out then.
I'll made a video to show you the stuttering: [www.youtube.com]
It even occurs if no filament is loaded. When I made that video I was able to turn the wheel by hand and extrude without a problem. Could there be anything wrong with the motor or is it possible that this is a wiring issue?

It looks like only one coil is being driven. Most likely an intermittent connection. Try measuring the resistance across the Melzi terminals and moving wires to see if you can find something loose.

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[www.hydraraptor.blogspot.com]

You were right, it is a wiring issue. But is a kinda strange one: I cant measure a connection for the green wire from the screw terminal of the melzi to the screw terminal of the extruder pcb. But I can measure connections between the melzi connector and the pin in the female extruder connector and between the screw terminal of the extruder pcb and the pin on the male extruder connector. So it seems that there is a problem with the connection of these 2 pins. Any ideas?
Right now I worked around this by striping a new green wire between the pcb and the melzi. Is the extruder connector for on the flat cable side a standard one? Or is is something specific to fit into the casing?

Edited 1 time(s). Last edit at 10/17/2014 09:00AM by laubraupe.

You might try pinching the IDC connector together again. It might be a connection that only makes when the cable is flexed due to inadequate crimping.

Regards,
Neil Darlow

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

Yes I can't see how the connector pins would not mate but people do mess up the IDC crimping. Either the cable not through enough to reach the back pins, at an angle, or not closed fully with a vice.

The connector is fairly standard although I can imagine some might be too big at the back for the casing.

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[www.hydraraptor.blogspot.com]